Great job!  I couldn't tell this was an experiment in first person PoV, it felt like you were quite experienced in the perspective.

In the interest of providing constructive criticism, one advantage to first person is the ability to lean into the character's thoughts, goals, and opinions as part of the description or exposition.  You can also help characterize them through your diction.  It's not necessary, but it's worth considering for the future.  For example, let me copy your second paragraph here, then make a few edits that wouldn't work so well in third person, but thrive in first person.

Directly above me, a woman grinded against our revered pillar, her slender legs stretching up on either side of me. She stood around a third of the pillar’s height, her arms unable to reach fully around the circumference. But that didn't keep her hips from bucking against the throbbing tree trunk. Every couple seconds, I felt more of her arousal drip onto my head, her tangy aroma mixing with the ambient odor of the giant I stood on.

Right above me swayed a blonde bombshell, with the firm ass and legs for days that coulda stepped outta one of my titty mags.  I felt myself drool a bit as she ground that sopping cunt against the towering cock, my mind still reeling that she'd need to pile on a few friends to reach the tippy top.  She leaned forward to wrap her arms around the god cock, and not only could I see her squish those sick-ass sweater yams, but I could still see her hands on both sides.  She couldn't hope to hug that super stiffy.  Even so she gave me a hell of a show, bucking against the cock like she was high on blow and hadn't been fucked in, like, a week.  The humping pinup was so wet I could feel it, splashing with every thrust and washing me in the only shower that could match a man as dirty as me.  Fuck, the heady aroma made me feel like I was back on spring break, between the man musk all around me beat out by the scent of a real woman.

So, that was hardly shakespear, but it conveyed some additional information about the person from who's perspective we watched the scene.  I definitely prefer your approach, especially for this shorter story, but maybe the example will be helpful in the future.

Either way, you have a solid scene here.  Really hot.  I'm a little surprised to see you step aoutside your more gentle wheelhouse, but you did well here.  I think my only disappointment with the PoV, is that we didn't get to see what happened woth the largest of the tiny women.  I'm just going to headcannon she gets used as a dildo.

Thanks again for sharing, great job on the story, and I'm looking forward to whatever you come up with next!